A dead bird found near downtown Danville last week tested positive for West Nile virus, becoming the town's first virus activity this summer and the San Ramon Valley's fourth confirmed case of the season, according to the Contra Costa Mosquito and Vector Control District.
Officials discovered the deceased American crow near the intersection of Verona Avenue and Love Lane last Tuesday. The Valley's other virus activity came in a dead bird in Blackhawk on July 31 and two more in Alamo on Aug. 4 and 7, respectively, according to the district.
"It's the time of year when mosquitoes become less picky about their blood source, and they tend to bite people as well as birds," Steve Schutz, Ph.D., scientific program manager with the district, said in a statement.
No human cases have been reported in county to date this year.
"West Nile virus is a disease of birds whose blood these mosquitoes normally prefer," Schutz added. "But, as many birds are beginning to migrate and their young have left the nest, mosquitoes, desperate to reproduce before the weather starts growing cooler, will bite people if they are present. They require protein from blood in order to produce their eggs."
The district also reported other West Nile virus activity in Contra Costa County in the previous week, with four other dead birds among Concord, Oakley and Pleasant Hill and two sentinel chickens from Holland Tract near Knightsen all testing positive.
In all, the county has recorded 26 virus-positive tests among birds, mosquitoes and sentinel chickens since June.
In humans, most cases of the virus are mild and include symptoms such as fever, headache, tiredness, body aches and swollen lymph glands, according to district officials. Severe cases of West Nile virus can be fatal. The most recent Contra Costa County human fatalities from the virus occurred in 2006, when two people died, officials said.
Birds are the reservoir for West Nile virus, which can be transmitted to humans via mosquitoes.
The two species of mosquitoes in the county capable of transmitting the virus prefer to feed on birds, but people can become infected when a mosquito bites an infected bird and then a person, district officials said.
The district preaches prevention, encouraging people to wear mosquito repellents, avoid going outside at dawn or dusk when mosquitoes are often present, dump or drain standing water where mosquitoes could lay their eggs, and report dead birds and neglected swimming pools.
For more information, visit the district's website.